Poultry are conventionally slaughtered by first electrically stunning each bird in turn and then killing the stunned birds by cutting their necks. The purpose of stunning is to ensure that the birds feel no pain when they are killed. The electrical stunning procedure involves removing birds from a transport crate, individually shackling them by their legs, conveying each shackled bird to an electric stunning bath in which the head of the bird is immersed in water which acts as the live electrode and current passes through the bird to earth via the shackle. The electrical stunning itself causes electroplectic convulsions, which result in haemorrhaging in the muscles of the breast and legs, and broken bones in the carcasses, particularly in the collar region. These conditions can lead to downgrading of poultry carcasses. Moreover, under the present commercial practice, the electrically stunned birds are processed mechanically and stored overnight typically up to 18 hours in a chiller, before the carcasses are either portioned or deboned for the retail market. If deboning is performed earlier, for example on the day of slaughter, then the muscles contract resulting in tougher meat. It is believed in the art that to avoid the problem of muscle contraction, post mortem glycolysis in the carcasses needs to be substantially completed before the steps of deboning and forming portions (`portioning`) can be performed without there being a resulting toughening of the meat upon cooking.